Fluidic ejection heads are useful for ejecting a variety of fluids including inks, cooling fluids, pharmaceuticals, lubricants and the like. A widely used fluidic ejection head assembly is in an inkjet printer.
With reference to FIG. 1, a representative portion of an exemplary and simplified prior art fluidic ejection head 10 is provided. As shown, the primary components of a fluidic ejection head 10 are a nozzle plate 12 attached, such as by adhesive 14, to a surface 16 of a semiconductor substrate 18. The semiconductor substrate 18 is preferably made of silicon and contains various passivation layers, conductive metal layers, resistive layers, insulative layers, and/or protective layers. Fluid ejection actuators 20, such as thermal actuators or piezoelectric actuators, are provided on the substrate surface 16. For thermal actuators, individual heater resistors are defined in the resistive layers of the nozzle plate 12 and each heater resistor corresponds to a nozzle hole 22 in the nozzle plate 12 for heating and ejecting fluid from the fluidic ejection head 10 toward a desired substrate or target.
Fluid receiving channels 24 and fluid chambers 26 for providing fluid to each of the ejection actuators 20 of the fluid ejection head 10 are either formed in the nozzle plate material or in a separate film layer. Upon activation of fluid ejection actuators 20, fluid is supplied to the fluid receiving channels 24 and fluid chambers 26 from a fluid feed channel 28 or fluid via that is in fluid communication with a fluid storage supply (as represented in FIG. 3). The fluid feed channel 28 is typically formed by chemically etching, dry etching, or grit blasting through the semiconductor substrate 18. The fluid receiving channels 24, fluid chambers 26, and fluid feed channel 28 of the fluidic ejection head 10 are collectively referred to herein as a “fluid supply channel.”
Referring to FIG. 2, a nozzle plate 12 of a fluid ejection head 10 typically contains hundreds of microscopic nozzle holes 22 for ejecting fluid therefrom. A plurality of nozzle plates 12 are typically fabricated in a polymeric film using laser ablation or other micro-machining techniques. Individual nozzle plates 12 are excised from the film, aligned, and attached to a plurality of substrates 18 on a multi-chip wafer so that the nozzle holes 22 align with the ejection actuators 20.
Referring to FIG. 3, an exemplary inkjet printing cartridge is shown with a fluidic ejection head 10 attached to a fluid storage supply 30. The fluid storage supply 30 includes a flexible circuit 32 containing electrical contacts 34 thereon for providing control and actuation of the fluid ejector actuators 20 on the substrate 12 via conductive traces 36. One or more fluid storage supplies 30 with attached fluidic ejection heads 10 may be used in a fluidic dispensing device, such as an inkjet printer, to provide control and ejection of fluid from the ejection heads 10 onto a target media.
One of the major variables in the operational efficiency of a fluidic ejection head 10 is controlling the viscosity of the fluid ejected from the nozzles 22. In this regard, many of the ejection fluids of a fluidic dispensing device contain pigments, dyes, and other volatiles. As the volatiles evaporate, the viscosity of the fluid in the fluid storage supply 30 become too viscous to be accurately and efficiently ejected. The rate and amount of evaporation of the volatiles is directly affected by the temperature and humidity of a local environment surrounding the fluidic ejection head 10. For purposes of the present disclosure, the “local environment” is considered the area adjacent nozzles 22 generally between the fluidic ejection head 10 and the target media when the target media is loaded in the fluid dispensing device. Similarly, another cause of failure of a fluidic ejection head 10 is fluid drying on the ejection head's nozzles 22 and the corresponding fluid supply channel.
While one known solution to prevent evaporation of the volatiles and drying of the fluid is to provide a cap or seal that covers the nozzles 22 of the fluidic ejection head 10 when the device is not in use, fluidic ejection heads 10 are often disposed in a small and/or closed environment (such as an inkjet printer) that makes it difficult to cover the nozzles 22. Further, even when the ejection head 10 is capped or sealed, the seal is often ineffective, particularly in long periods of inactivity of the fluidic dispensing device.
Accordingly, what is desired is a fluidic dispensing device that promotes improved efficiency in ejecting fluid by maintaining desired humidity levels at the local environment surrounding the device's fluidic ejection heads.